1. Field of the Invention
The present invention relates to a current detecting circuit for an X-ray tube.
2. Description of the Related Art
Heretofore, a circuit as shown in FIG. 9 has been used as a high-voltage current detecting circuit for detecting a current of an X-ray tube. Referring to FIG. 9, a high-frequency inverter 1 is connected to a high-voltage transformer 2, which has secondary windings 22 and 23, which produce a high-frequency output at a higher voltage. The secondary windings 22 and 23 have equal numbers of turns to each other, and a center tap is grounded at a point 25.
The voltage across the secondary windings 22 and 23 is rectified by a high-voltage rectifier 4, which has a positive output terminal connected to an anode 74 of the X-ray tube 7 and a negative output terminal connected to one terminal 72 of a filament of said X-ray tube 7. An AC voltage source 11 is connected to an isolation transformer 3 having a primary winding 31 and a secondary winding 32. The secondary winding 32 is connected to filament terminals 71 and 72 of the X-ray tube 7. Current passing through the X-ray tube 7 can be measured and detected at any point of A, B, C and D. In case of the point A or B, it is required to provide a high voltage insulation for a detecting device or the like. In case of the point C, it is possible to detect the current by rectifying the current by a rectifier circuit, but in this case it is required to provide a high insulation for the detecting device or the like. In case of the point D, which is connected to the center tap, it is required to rectify the current by a rectifier circuit in order to detect the current. However, in this case a stray current may pass through the detecting circuit simultaneously with a current to be detected, because stray capacity is formed between the windings 22 and 23, causing a current for charging or discharging them. The stray current is so high that it is not negligible in the case where the high frequency inverter is employed.
Thus, it will be understood that the current detecting system heretofore proposed presents important problems in providing high insulation and high precision of measurement.